An anisotropic bonded magnet (referred also to as “bonded magnet” hereinafter), which is obtained by compressively molding a compound comprised of rare-earth anisotropic magnet powder and binder resin, has various advantages such as that a large magnetic flux density can be obtained even in small size and the degree of freedom is large in molding, for example, in making a thin magnet. For this reason, demand for bonded magnets is increasing as permanent magnets for field magnets to be used for multi-pole motors, which are required to output high power and conserve energy as well as to be reduced in size and weight. In accordance with such an increase in demand, request for reducing the cost of bonded magnets is also growing.
Rare elements (such as rare-earth elements) as the main raw materials for bonded magnets may not be available in low cost. In this regard, in order to allow for price reduction, it is important to enhance the mass production ability for bonded magnets. In particular, it may be important to reduce an amount of time required for producing one bonded magnet (so-called takt time). For reducing the takt time, it is effective to improve the efficiency in alignment step (magnetic alignment step) and molding step (referred also to as “molding step in magnetic field” in combination), which require long time for one step (process time), among production steps for bonded magnets.
Here, the alignment step is a step that applies a magnetic field (aligning magnetic field) to a compound filled in a cavity of a molding die thereby to align constituent particles of the anisotropic magnetic powder in directions of magnetization easy axes. Rare-earth anisotropic magnet powder in itself fundamentally has large magnetic coercive force and sometimes may thus be difficult to be aligned. However, constituent particles thereof (referred also to as “magnetic particles” hereinafter) are enabled to rotate or move in the softened or molten binder resin, so that the magnetization easy axes of crystals are to be aligned to the direction of the aligning magnetic field. Such an alignment step is necessary for obtaining an anisotropic bonded magnet with high magnetic flux density. However, unlike a magnetizing step and an incorporating step, each process of softening the binder resin such as by heating the compound and aligning (moving) the magnetic particles requires necessarily a commensurate amount of time. Therefore, it is difficult to significantly reduce the takt time merely by reducing the process time of the alignment step.
To this end, it is effective for reducing the takt time to increase the number of objects to be processed in one alignment step (to perform so-called multiple cavity process) thereby reducing the average process time for one bonded magnet. For this operation, if the conventional facilities are drastically changed or the apparatus is scaled-up, the production cost is rather raised and bonded magnets may not be produced in low cost. Accordingly, in order to increase the number of objects to be processed in the molding step in magnetic field while taking advantage of the conventional facilities, it is effective to reduce the size of processing space required for one bonded magnet (compact thereof). In this respect, it may be considered to substitute a permanent magnet for a conventionally used magnet coil (electromagnet) to apply the aligning magnetic field.